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Article with multiple surface depressions and method and system for making the same


Title: Article with multiple surface depressions and method and system for making the same.
Abstract: Articles having multiple surface depressions and process and apparatus for making the same. The invention is useful in making, inter alia, glass plates having a surface depression array which can be used in semiconductor and electronics manufacture, drug discovery and display devices. ...


USPTO Applicaton #: #20100326972 - Class: $ApplicationNatlClass (USPTO) -
Inventors: Xinghua Li, Mark Lawrence Powley, Robert Stephen Wagner



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The Patent Description & Claims data below is from USPTO Patent Application 20100326972, Article with multiple surface depressions and method and system for making the same.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser. No. 11/820,514, filed on Jun. 20, 2007, having the same title and which claims priority to U.S. Provisional Patent Application Ser. No. 60/840,567, filed on Aug. 28, 2006, entitled “ARTICLE WITH MULTIPLE SURFACE DEPRESSIONS AND METHOD AND SYSTEM FOR MAKING THE SAME,” the contents of which are relied upon and incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

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The present invention relates to articles having a plurality of surface depressions, and method as well as apparatus for making the same. In particular, the present invention relates to articles such as glass plates having micro depression arrays, laser ablation process for making the same and apparatus for making the same involving laser ablation.

BACKGROUND OF THE INVENTION

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Articles having a surface with arrays of depressions are widely used in various industries, ranging from information display, drug discovery, microlithography, to printing and others. The depressions may form two-dimensional arrays with various patterns in which various materials can be placed, processed or further disposed of.

Fabrication of articles with surfaces having relatively large depressions on the centimeter and millimeter scale can be done by, e.g., carving, pressing, molding, mechanical drilling, and the like. However, when the dimensions of such depressions are required to be on the micron meter scale, ranging from several micrometer to several hundred of micrometers, those methods usually cannot be effectively utilized, especially where a large array of depressions are required to have essentially uniform sizes and to be precisely aligned to each other. This is especially true with regard to creating depression arrays on hard materials that require high processing temperatures, such as inorganic glass and glass-ceramic materials. Moreover, mechanical machining typically would result in poor surface quality of the depressions. Where low surface roughness of the depressions is desired, further surface finishing steps such as etching may be required.

In an effort to fabricate articles with surface depression arrays on the micrometer scale based on inorganic glass, lithographic processes may be used. As in the semiconductor industry, the surface is covered with a layer of photoresist film, then selectively exposed to lithographic irradiation, followed by etch, resist stripping and cleaning, whereby a plurality of etched depressions can be formed on the surface. This method is effective in creating depressions that form a predetermined pattern on the surface, and the outer diameter of the depression can be relatively precisely controlled.

However, the lithographic approach suffers from the following drawbacks. First of all, the etching process typically requires the use of etching solutions specific to the substrate material. For example, for SiO2-containing inorganic glass, HF.NH4F solution is a typically used etching solution. Waste disposal in such etching process is a significant challenge. Moreover, the lithographic process requires multiple steps including resist applications, etch, resist stripping, and complex equipment such as the lithographic tools, and is thus inherently costly.

Still another problem of the lithographic approach is the lack of ability to produce certain shape of the depressions. Generally, when a piece of glass is etched, especially where wet etch is used (which is what is used in most cases), the material is removed non-discriminatively in all directions of the surface in contact with the etching solution (i.e., isotropic etch). As is known in the art of lithography, this typically results in undercutting of the substrate under the film on the top of the substrate. Such undercutting is usually highly undesirable if the film (such as a layer of metal) is desired to be retained on the top of the substrate surface. In cases where the film is not to be retained (such as where the film is a layer of photoresist), the end result would be a depression with outer diameter larger than that of the exposed area, and an outer diameter to depth ratio of higher than 2:1. It is difficult, therefore, to obtain depressions with smaller outer diameter-to-depth ratio. This means that, where the desired outer diameter of the depression is pre-determined, it would be difficult to obtain depressions with larger cavity volume. Due to the inflexibility of the outer diameter to depth ratio of the wet etch process, it would be difficult to create depressions with a wide range of outer diameter to depth ratios.

Yet another drawback of the lithography approach is the need of creating a mask prior to lithography, which is usually a costly extra step. Image of depression patterns are first recorded into a precision mask, which is then used as the source of the depression pattern information to be formed on the article surface. While for large volume production the cost of the mask can be shared and mitigated among the many products, for relatively small-scale production, the cost of the mask can lead to prohibitively high final cost for the final product, and the formation of the mask can delay the production of the final product as well.

Therefore, there remains a genuine need of a process for making articles having a surface bearing a plurality of depressions without the drawbacks of the methods described above. There is also a genuine need of articles having a surface bearing a plurality of depressions having high surface quality yet dimensions typically not obtainable by wet etch.

SUMMARY

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OF THE INVENTION

Accordingly, a first aspect of the present invention is an article having a surface bearing a plurality of depressions having an outer diameter of not larger than 500 μm and an outer diameter to depth ratio of smaller than 2. In certain embodiments of the article of the first aspect of the present invention, the depressions have a fire-polished surface.

A second aspect of the present invention relates to an article having a surface bearing a plurality of depressions having an outer diameter of not larger than 500 μm, wherein the depressions have fire-polished surface. In certain embodiments of the article of the second aspect of the present invention, the depressions have an outer diameter to depth ratio of smaller than 2.

In certain embodiments of the article of the first and/or second aspects of the present invention, the depressions have an outer diameter to depth ratio smaller than 2, in certain embodiments smaller than 1.5, in certain other embodiments smaller than 1.0, in certain other embodiments smaller than 0.8, in certain other embodiments smaller than 0.5.

In certain embodiments of the article of the first and/or second aspect of the present invention, the diameter of the cross-section of each individual depression essentially normal to the direction of the depth thereof decreases in the direction from the article surface to the bottom of the depression.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the outer diameter to depth ratios of the depressions vary. In certain embodiments, they may vary from 3.0 to 0.5.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions form at least one array.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions have a surface roughness of less than 5 nm, in certain embodiments less than 1 nm, in certain embodiments less than 0.5 nm, in certain embodiments less than 0.1 nm.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions are formed by directing a laser beam to the surface area where a depression is desired.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the article is a plate having at least one major surface, and wherein the depressions are formed on at least one major surface.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the article is made of inorganic glass, glass-ceramic or crystalline materials.

According to certain embodiments of the article of the first and/or second aspects of the present invention, at least the material forming the surface bearing the depressions has a melting point of not lower than 500° C., in certain embodiments not lower than 800° C., in certain other embodiments not lower than 1000° C., in certain embodiments higher than 1200° C., in certain embodiments higher than 1500° C. In certain embodiments, the surface material is a glass or glass-ceramic comprising at least 80% by weight of silica, in certain embodiments at least 90%, in certain embodiments at least 95%. In certain embodiments of the article of the first and/or second aspects the surface region is made of silica.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions have a standard deviation of outer diameter not higher than 5 μm, in certain embodiments not higher than 3 μm, in certain other embodiments not higher than 1 μm, in certain embodiments not higher than 0.5 μm.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions have a standard deviation of depth of not larger than 5%, in certain embodiments not larger than 3%, in certain embodiments not larger than 1%, of the average depth of the depressions.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions have an essentially uniform diameter in the direction of the depth from the article surface to the bottom of the depressions.

According to certain embodiments of the article of the first and/or second aspects of the present invention, the depressions form an array having a plurality of rows and columns, and the spacing between the rows or columns is not larger than 2 times of the average outer diameters of the depressions. In certain embodiments, the spacing between the rows and the columns is not larger than 2 times of the average outer diameter of the depressions. In certain embodiments, the spacing between the rows or the columns is essentially uniform.

According to certain embodiments of the article of the first and/or second aspects of the present invention, at least the surface region of which is made of a material having a coefficient of thermal expansion from 0 to 300° C. in the range of 0-40×10−7/° C., in certain embodiments in the range of 0-30×10−7/° C., in certain embodiments in the range of 0-15×10−7/° C., in certain other embodiments in the range of 0-8×10−7/° C., in certain other embodiments in the range of 1-4×10−7/° C.

A third aspect of the present invention is directed to a process for making an article having a surface bearing a plurality of depressions, comprising the following steps: (A) directing a laser beam to the surface area where a depression is desired; (B) allowing the laser beam to ablate the material in the surface area which is exposed to the laser beam, such that a plurality of depressions having an outer diameter not larger than 500 μm is formed.

According to certain embodiments of the process of the present invention, where thermal ablation is involved, the depression formed in step (B) has a fire-polished surface.

According to certain embodiments of the process of the present invention, in step (B), the time of ablation is sufficiently long such that at least part of the depressions formed have an outer diameter to depth ratio of lower than 2, in certain embodiments lower than 1.5, in certain embodiments lower than 1, in certain embodiments lower than 0.8, in certain other embodiments lower than 0.5.

According to certain embodiments of the process of the present invention, the depressions are formed by a single laser beam operating repeatedly at differing locations. In certain other embodiments, the depressions are formed by a plurality of laser beams operating at least partially simultaneously.

According to certain embodiments of the process of the present invention, the depressions formed in step (B) have a surface roughness of less than 5 nm, in certain embodiments less than 1 nm, in certain embodiments less than 0.5 nm, in certain embodiments less than 0.1 nm.

According to certain embodiments of the process of the present invention, the article is a plate having at least one major surface, and wherein the depressions are formed on at least one major surface.

According to certain embodiments of the process of the present invention, the article is made of inorganic glass, glass-ceramic or crystalline materials.

According to certain embodiments of the process of the present invention, the surface to be ablated of the article is made of a material having a melting point of not lower than 500° C., in certain embodiments now lower than 800° C., in certain embodiments not lower than 1000° C., in certain embodiments not lower than 1200° C., in certain embodiments not lower than 1500° C., and the ablated surface area is heated to a temperature higher than the melting point of the material at least partly by the laser beam.

According to certain embodiments of the process of the present invention, the depressions formed in step (B) have a standard deviation of outer diameter not higher than 5 μm, in certain embodiments not higher than 3 μm, in certain other embodiments not higher than 1 μm, in certain embodiments not higher than 0.5 μm.

According to certain embodiments of the process of the present invention, the depressions have a standard deviation of depth of not larger than 5%, in certain embodiments not larger than 3%, in certain embodiments not larger than 1%, of the average depth of the depressions.

According to certain embodiments of the process of the present invention, the diameter of the cross-section of individual depressions essentially normal to the direction of the depth thereof decreases in the direction of the depth from the article surface to the bottoms of the depressions.

According to certain embodiments of the process of the present invention, the depressions created in step (B) form at least one array, and the spacing between the rows or columns are not larger than 2 times of the average outer diameters of the depressions. According to certain embodiments of the process of the present invention, the spacing between the rows and the columns are not larger than 2 times of the average outer diameter of depressions. According to certain embodiments of the process of the present invention, the spacing between the rows and columns are essentially uniform.

According to certain embodiments of the process of the present invention, at least the surface region of the article to be ablated is made of a material having a coefficient of thermal expansion from 0 to 300° C. in the range of 0-40×10−7/° C., in certain embodiments in the range of 0-30×10−7/° C., in certain embodiments in the range of 0-15×10−7/° C., in certain other embodiments in the range of 0-8×10−7/° C., in certain other embodiments in the range of 1-4×10−7/° C.

According to certain embodiments of the process of the present invention, the laser is selected from the group consisting of: CO2 laser, YAG laser, UV excimer laser.

According to certain embodiments of the process of the present invention, the surface area directly exposed to the laser beam has a diameter of less than 200 μm, in certain embodiments less than 150 μm, in certain embodiments less than 100 μm, in certain embodiments less than 50 μm.

A fourth aspect of the present invention is a system for forming a plurality of depressions on a surface of an article, comprising the following components: (i) a laser generator; (ii) a laser focusing device capable of providing a laser beam directed to the surface of the article on which the depressions are to be formed; (iii) a stage on which the article is to be placed for laser ablation; and (iv) a device capable of moving the laser beam relative to the surface of the article to be ablated.

Certain embodiments of the present invention have one or more of the following advantages. First, the articles of certain embodiments of the present invention can have depressions with various geometry and dimensions achievable by laser ablation, particularly with various outer diameter to depth ratios. Especially, the depressions can have an outer diameter to depth ratio of smaller than 2, which is difficult to achieve in the traditional lithographic process. Yet, the depressions of the article of the present invention can have a very low surface roughness, which is desired in many applications. The article of the present invention can be based on various materials, including plastic, inorganic glass, glass-ceramic materials, and crystalline materials, depending on the end application. Second, as to the process and apparatus system of the present invention, they have the flexibility to be applicable for substrates made of various materials ranging from organic polymers, inorganic glass materials, glass-ceramic materials and crystalline materials; they can be used to produce depressions with various outer diameter to depth ratio; they can be used to produce various overall depression patterns on the surface of the article to be ablated; and they can be realized by using relatively inexpensive commercial laser generators such as CO2 lasers.

Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.

It is to be understood that the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

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In the accompanying drawings:

FIG. 1 is a schematic illustration of the cross-section of a glass plate bearing depressions formed by wet etch;

FIG. 2 is a schematic illustration of the cross-section of a glass plate bearing conical depressions according to an embodiment of the present invention;

FIG. 3 is a schematic illustration of the cross-section of a glass plate bearing truncated-conical depressions according to another embodiment of the present invention;

FIG. 4 is a partial picture of the surface of a glass plate bearing depressions formed by the laser ablation process of the present invention;

FIG. 5 is a schematic illustration of the apparatus set-up of one embodiment of the present invention;

FIG. 6 is an illustration of the typical pulse train of a CO2 laser used in the examples of the present application;

FIG. 7 is a schematic illustration of the apparatus set-up of another embodiment of the present invention; and

FIG. 8 is a schematic illustration of the apparatus set-up of another embodiment of the present invention.

DETAILED DESCRIPTION

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OF THE INVENTION

Unless otherwise indicated, all numbers such as those expressing weight percents of ingredients, dimensions, and values for certain physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” It should also be understood that the precise numerical values used in the specification and claims form additional embodiments of the invention. Efforts have been made to ensure the accuracy of the numerical values disclosed in the Examples. Any measured numerical value, however, can inherently contain certain errors resulting from the standard deviation found in its respective measuring technique.

As used herein, in describing and claiming the present invention, the use of the indefinite article “a” or “an” means “at least one,” and should not be limited to “only one” unless explicitly indicated to the contrary. Thus, for example, reference to “a depression” includes embodiments having two or more depressions, unless the context clearly indicates otherwise.

“Melting point” as used herein denotes the melting point under atmospheric pressure of a crystalline material, or softening point of a glass material, as the case may be.

As used herein, “depression surface” or “surface of a depression” means the wall surface of the depression.

As used herein, “glass consisting essentially of silica” means a glass material comprising, by weight, at least 80 weight % (wt %) silica.

As mentioned supra, articles having a surface bearing a plurality of depressions are used widely in various industries. While mechanical approaches and in situ formation of the depressions during the formation of the articles per se can be used for articles with a small number of relatively large depressions, they become economically non-viable when a large number of small depressions are required. Such small depressions are sometimes called cavities on the article surface.

Depending on the end use of the article bearing depressions, the depressions may be required to take various geometry and dimension, and may be required to have various degree of precision alignment. The depression, when intersected by a plane tangential to the surface on which the specific depression is formed, shows a cross-section thereof in the form of a closed curve. As used herein, the longest straight-line distance between any two points in this cross-section is the outer diameter of the depression. The length of a straight line segment from the lowest point of the depression to the plane tangential to the surface of the article, perpendicular to the plane tangential to the surface of the article, is regarded as the depth of the depression. The direction normal to the plane tangential to the surface of the article is called the direction of depth of depression. Thus, if the depression is a cylindrical cavity formed under a flat surface, the cross-section of the depression when intercepted by the surface plane would be a circle, and the outer diameter of the depression would be the diameter of the cylindrical surface of the depression. For another example, where the depression is an elongated cube formed under a flat surface, the cross-section of the depression when intercepted by the surface plane would be a rectangle, and the outer diameter of the depression would be the length of the diagonal line of the rectangular cross-section.

A plurality of depressions may form multiple rows and columns, forming a complex matrix, which is sometimes called a “microcavity array.” The depressions in a micro-cavity array may be required to have an outer diameter ranging from 1 μm to 500 μm for various products. The arrays of depressions may form various patterns as well depending on the final use of the articles. For example, in the area of printing, pigments and/or dye solutions may be dispensed into the cavity array, and subsequently transferred onto the surface of the receiving media, such as paper, boards, fabric, and the like, to effect the printing of an image. For another example, dozens, hundreds and sometimes thousands of depressions in the cavity array may be filled with a certain fluid containing an antibody first, which is subsequently filled with samples of fluid to be tested. The differing reaction results in the large number of depressions can be revealed by various means, then collected and analyzed.

A natural solution for making the micro-cavity arrays on the surface of an article is lithography, which is currently used in relation to glass, glass-ceramic and ceramic based substrates. Lithography processes used typically requires wet etch by chemical solutions, as mentioned supra. With amorphous glass, glass-ceramic and ceramic substrates, the etching process is sometimes a multi-step undertaking and difficult to control in order to produce large variations in cavity volume. In addition, as mentioned supra, in isotropic etching processes (which are mostly the actual etching cases) of a flat substrate, the depressions eventually formed would usually take a semi-spherical or semi-ellipsoidal shape. FIG. 1 shows the cross-section of a typical depression formed by lithography. In this figure, 101 is a substrate in which semi-spherical surface depressions 103 are formed. The depressions have an outer diameter D and a depth R where D≧2R. In situations where D is pre-determined, the depth of the depression is limited to less than ½D, hence the volume of the depression is generally limited to less than 0.125π·D3. This is not desirable in many applications which would require deeper depression and larger volume thereof.

In certain applications, it is highly desired that the depressions have a conical shape or truncated conical shape, i.e., along the direction of the depth of the depression, from the surface of the article to the bottom of the depression, the area of the cross-sections obtained by intercepting the depression with planes parallel to a plane tangential to the article surface gradually decrease. FIG. 2 illustrates the cross-sectional view of a plate substrate 201 having cone-shaped depressions 203 with an outer diameter of D and a depth R. FIG. 3 illustrates the cross-sectional view of a plate substrate 301 having truncated cone-shaped depressions 303 with an outer diameter of D and a depth of R. In lithography process involving isotropic etch, the depressions illustrated in FIGS. 2 and 3 are difficult to obtain. As discussed above, if D<2R is required, the lithography approach with isotropic etch, alone, cannot be used to achieve these results. The edge (i.e., the area where the depression wall meets the main surface of the substrate on which the depressions are formed) of the depressions as illustrated in FIGS. 2 and 3 is angular. In practice, such edge can be rounded due to the melting and flowing of the material in that area.




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stats Patent Info
Application #
US 20100326972 A1
Publish Date
12/30/2010
Document #
12787680
File Date
05/26/2010
USPTO Class
21912169
Other USPTO Classes
International Class
23K26/00
Drawings
5


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